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The head of Samoa Air has defended its policy of charging passengers by their weight, arguing such a system is not only fair but the future for other airlines.

"The next step is for the industry to make those sort of changes and recognize that 'Hey, we are not all 72 kilograms (about 160 pounds) anymore and we don't all fit into a standard seat,''' Chris Langton, Samoa Air chief executive told CNN.

"What makes airplanes work is weight. We are not selling seats, we are selling weight."

Langton said Samoa Air's policy went into effect in November for domestic fliers and in the "past few weeks" for international routes.

According to the airline's website, "your weight plus your baggage items is what you pay for. Simple."

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The South Pacific air carrier flies just three aircraft, two 10-seaters and one four-seater and serves Samoa, American Samoa, Tonga, Niue, Tokelau, the North Cook Islands and Wallis and Futuna islands in French Polynesia. Langton said the company is planning to purchase a much larger Airbus A320-200 this year for service to international destinations in the region including Australia, New Zealand and Fiji.

"Customers are getting their heads around the concept that paying by weight is the fairest way of doing it," Langton said.

"It's always going to be a sensitive issue, we try to keep it lighthearted and try to keep people on the positive side, particularly for those that are carrying a fair bit of bulk."

"It works both ways. People who pay more deserve more. ... So, it is in our interests that we take care of the people that who've chalked in at 150, 180 kilograms (330, 396 pounds). They've paid their fare and the we try to give them what they should have, which is a comfortable seat. We try to make sure they have space around them, that taller people have got more leg room -- within the confines of the airplane these days we try to do it."

World first

Samoa Air says its program is the world's first fare structure that charges only by weight.

To book online, travelers enter their approximate weight and that of their luggage and prepay based on that "guesstimate." The airline is not equipped to process payments online, but that service is coming soon, Langton said.

Passengers and their luggage are weighed again at the airport.

And if your weight and that of your bags exceed your booking weight? Langton said the airline has a "fiddle factor" of about 2%. So Samoa Air will let a few kilos slide, but the airline is unlikely to provide a refund if passengers roll up to the tarmac with a lighter load.

Langton said families have been pleased with the pricing model because it often costs less to fly with children using the pay-by-weight model than it would to purchase flat-fare seats.

"People deserve to be able to travel in comfort, and the industry has been trying to fit all the square pegs into round holes and hasn't been taking into account that for a lot of people, traveling by air is an uncomfortable experience," he said.

"It is not the fun thing you used to do in the past. You don't really look forward to a flight these days for one reason or another and its usually to do with the comfort factor. You are either squeezed into a narrow seat if you are a bigger person or you have got maybe bigger people hanging over you if you are a smaller person."

"Either way both people are being disadvantaged. The larger person is not getting the credit of being large and being catered to because the fare is considered to be equal based on seats but we know it is not. It is always based on weight."

Some travelers have criticized the weight-based fare concept as a "fat tax." Others say they believe it's only fair.

"Yes, if I am getting less than 100% of the seat I paid for, the person taking my space should have to make up the difference," a CNN.com commenter wrote.

Some major U.S. airlines have policies for passengers of size, requiring those who do not fit into a seat comfortably to buy a second seat.

For a tiny carrier like Samoa Air, the fare model seems reasonable, according to airline analyst Vaughn Cordle, a partner at Ionosphere Capital.

"For this small operation, specifically with the aircraft they fly, weight restrictions are the key practical problem they have to deal with on every flight. They have a solid business case to charge for weight," Cordle said.

"The nature of their business model, island-hopping with a small aircraft, they have to do it. The alternative is to charge more on a flat rate, and then everyone is discriminated against. Makes sense to not penalize a lighter-weight passenger. The cost per pound is so high on those light airplanes."

But air travelers are unlikely to see anything like it on a large U.S. airline, he said.

"For U.S. airlines, I think this is an issue they will not touch with a 10-foot pole because of the negative publicity and the practical purposes of weighing people at the gate."